1. Field of the Invention
The present invention relates to an image pickup apparatus.
2. Related Background Art
FIG. 1 is a block diagram which illustrates a digital electronic camera.
Referring to FIG. 1, reference numeral 200 represents a digital electronic camera, and 201 represents a recording medium, such as a memory card. In the digital electronic camera 200, reference numeral 1 represents a shutter 1 also serving as a diaphragm, 2 represents an optical low pass filter, and 3 represents a drive circuit for each mechanical portion. Reference numeral 4 represents an image pickup device for converting light reflected by an object into an electric signal, 6 represents a timing signal generating circuit (hereinafter called a xe2x80x9cTGxe2x80x9d), 5 represents an image pickup device drive circuit for amplifying a signal transmitted by the timing signal generating circuit to a level which permits the image pickup device to be driven, 7 represents a pre-processing circuit comprising a CDS circuit for eliminating noise included in the output from the image pickup device 4 and a circuit for non-linearly amplifying the output before the output is A/D converted, 8 represents an A/D converter, 11 represents an image pickup signal processing circuit, 12 represents a signal process controlling CPU for controlling the image pickup signal processing circuit, 13 represents a CPU for controlling the mechanical portion and a control portion, 14 represents a control display portion for indicating displays for aiding operations of a user and states of the camera, and 15 represents a control portion for controlling the camera from outside. Reference numeral 18 represents a recording medium I/F (interface) for establishing the connection between the digital electronic camera 200 and the recording medium 201.
FIG. 2 is a diagram which illustrates the image pickup signal processing circuit 11. Reference numeral 101 represents a color separating circuit for separating the output signal from the image pickup device into color signals, 102 represents a color matrix circuit for deducing R, G and B signals from the color-separated signals, 103 represents a WB correction circuit for correcting the levels of the R, G and B signals in accordance with the color of a light source of light that irradiates the object, 104 represents a color difference signal deducing circuit for deducing color difference signal R-Y and B-Y from the corrected R, G and B signals, 105 represents a low-frequency brightness signal correction value deducing circuit for deducing a signal for correcting the color component ratio of the brightness signal from the corrected R, G and B signals, 106 represents a color-modulated-portion trapping circuit for removing a color modulation signal that overlaps the image pickup signal, 107 represents a horizontal aperture circuit for highlighting the horizontal outline, 108 represents a vertical aperture circuit for highlighting the vertical outline, 109 represents an adder for adding the signals, and 110 represents a subtractor.
FIG. 3 is a diagram which illustrates the configuration of color filters of the image pickup device 4. FIG. 4 is a diagram which illustrates the operation timing of the image pickup device 4 and output signals from the image pickup device 4.
Referring to FIGS. 1 and 2, the conventional digital electronic camera will now be described.
When a photographer controls the control portion 15, the camera starts the photographing operation. In accordance with an intention of the photographer, a lens system (not shown) is controlled by the mechanical portion controlling CPU 13 and the mechanical system drive circuit 3. At this time, photographing conditions and so forth are displayed on the control portion 15 so that the state of the camera is provided to the photographer. Furthermore, a light measuring circuit (not shown) measures the brightness of the object. In addition, the diaphragm value and the shutter speed of the shutter 1 also serving as a diaphragm are deduced by the mechanical portion controlling CPU 13. In accordance with the control value deduced by the mechanical portion controlling CPU 13, the shutter 1 also serving as a diaphragm is operated by the mechanical system drive circuit 3. Thus, the image of the object is exposed to light and light reflected by the object is made incident upon the image pickup device 4 through a photographing lens (not shown) and the shutter 1. The shutter 1, at this time, limits the quantity of light incident on the image pickup device 4. In a case where an interlace reading CCD is employed as the image pickup device, the shutter 1 prevents an adverse influence of incident light on the signal charge. The image pickup device 4 is operated in response to a drive signal obtained by amplifying the output from the timing signal generating circuit 6 by the image pickup device drive circuit 5. The timing signal generating circuit 6 is controlled by the signal process controlling CPU 12. The output from the image pickup device 4 thus operated is supplied to the pre-processing circuit 7. The pre-processing circuit 7 performs a CDS (Correlated Double Sampling) process and a process for forming the picked up image into a non-linear shape for the purpose of effectively using the dynamic range of the A/D converter. The output denoting the pickup image is converted into a digital signal by the A/D converter 8, the digital signal being then supplied to the image pickup signal processing circuit 11. The image pickup signal processing circuit 11 performs a predetermined brightness signal process and a color signal process to be described later. Then, a process for converting the processed signal into a predetermined format (not shown) is performed, and the processed signal is recorded on the recording medium 20 through the I/F 18 for the recording medium.
The image pickup signal processing circuit 11 receives the output signal transmitted from the image pickup device thus A/D converted. The image pickup device has a color filter configuration as shown in FIG. 3 in which Mg (magenta), G (green), Y1 (yellow) and Cy (cyan) are disposed on each pixel. For example, field 1 is made to be an ODD field and field 2 is made to be an EVEN field. The two fields are read while interlacing one line and two lines are simultaneously read. Thus, the output from the image pickup device is formed into a signal obtained by linear-sequentially forming dot sequential signals (Mg+Y1) and (G+Cy) and dot sequential signals (G+Y1) and (Mg+Cy). The foregoing state is shown in FIG. 4. Referring to FIG. 4, (1) shows a vertical synchronizing signal, (3) shows a transference pulse for transferring each pixel signal to the vertical shift register in a case where the interline CCD is used and (4) shows the output signal from the CCD. In the image pickup signal processing circuit 11, the image signal is, by the color separating circuit 101, is separated into color signals c1 (a line sequential signal of (Mg+Y1) and (G+Y1)) and c2 (a line sequential signal (G+Cy) and (Mg+Cy)). The separated signals are linearly coincided by the color matrix circuit 102 and are converted into pure color signals R0, G0 and B0 by matrix calculations before they are supplied to the WB correction circuit 103. In the WB correction circuit 103, the color temperature of light source light that irradiates the object is corrected in response to a WB control signal supplied from the signal process controlling CPU 12. The corrected RGB signals are used to cause the color difference signal deducing circuit 104 to deduce the color difference signals R-Y and B-Y. The low-frequency brightness signal correction value deducing circuit 105 deduces correction signal YL in accordance with the RGB signals, the correction signal YL being used to correct the ratio of color components that constitute the brightness signal in order to improve the reproducibility of the brightness of the colors.
The image signal transmitted from the A/D converter is also supplied to the color-modulated portion trapping circuit 106 to decay the modulated color signals overlapped on the brightness signal. From the output from the color-modulated portion trapping circuit 106, highlighted aperture signals are deduced by the horizontal aperture circuit 107 and the vertical aperture circuit 108, the deduced aperture signals being added with a through brightness signal by the adder 109. The subtractor 110 subtracts a correction portion YL from added and deduced signal Y0 so that corrected brightness signal Y is obtained.
However, the conventional digital electronic camera involves the following problems.
(1) Since the digital electronic camera is designed to take a picture of a color and natural image, satisfactory performance cannot be obtained to take a picture of an object, such as characters, an illustration or a figure, the picture of which must be taken with a high resolution.
(2) Since photographed characters involve indentations and/or discontinuous portions, erroneous recognition cannot be prevented if bit map data of the characters are recognized by a recognizing software.
(3) In a case where an information apparatus, such as a computer, is used to make a deformed image, such as an illustration, from a natural image, a supplied natural image can easily have color and brightness irregularity. Therefore, heavy load is required to remove the irregularity on the information apparatus.
Accordingly, an object of the present invention is to provide an image pickup apparatus which is capable of overcoming the foregoing problems.
In the present invention, the following structures are employed:
(1) A mode for photographing a natural image and a monochrome and high resolution mode for photographing monochrome characters or an illustration are provided and the two modes can be switched.
(2) The monochrome and high resolution mode is performed by using at least any one of the following arrangements.
(1) An optical low pass filter is retracted from the optical passage or the characteristics of the optical low pass filter are changed.
(2) The color level of each pixel of the image pickup device with respect to the color of the object is obtained and the level is corrected for each color component to align the signal levels.
(3) An image pickup device of a non-interlace type of a combination of an interlace type image pickup device and a mechanical shutter is used to read information of all pixels exposed to light in the same time.
As a result of the foregoing structure (1), if the monochrome mode is selected, the retraction of the optical filter or the change of the characteristics of the same as shown in (1) prevents trapping of video information near the Nyquist frequency in a spatial sampling due to pixels that can be lost in the natural image photographing mode. Thus, a high resolution image can be obtained.
Since the portion modulated by the color components of the output signal from the image pickup device can be erased due to the color level correction (2), the necessity of disposing a band limiting filter, such as a trapping circuit, for removing the color modulated portion in the high frequency brightness signal processing system can be eliminated. Thus, video information in the high frequency range can be maintained and used as high resolution brightness information.
As a result of the structure (3), information of all pixels of the image pickup device which is free from time lag can be obtained. Therefore, high resolution video information can be obtained without an influence of camera shake and the movement of the object.
According to one aspect of the present invention, there is provided an image pickup apparatus comprising: image pickup means for converting an optical image into an electric signal; lens position changing means for changing the optical axial directional position of a focusing lens with respect to the image pickup means; and focal point evaluating value detection means for deducing a focal point evaluating value, which is made to be a maximum value in a focused state, in accordance with an output from the image pickup means, wherein two or more lens movement quantities by the lens position changing means can be set.
According to another aspect of the present invention, there is provided an image pickup apparatus comprising: image pickup means; switching means capable of switching between a first photographing mode in which an electric signal transmitted from the image pickup means is used to form a color natural image signal and a second photographing mode in which the electric signal transmitted from the image pickup means is used to form a white and black high resolution image signal; and focusing control means for precisely performing focal point adjustment in the second photographing mode as compared with the first photographing mode in accordance with the photographing mode switching operation performed by the switching means.
According to another aspect of the present invention, there is provided an image pickup apparatus comprising: an image pickup means; switching means capable of switching between a first photographing mode in which an electric signal transmitted from the image pickup means is used to form a color natural image signal and a second photographing mode in which the electric signal transmitted from the image pickup means is used to form a white and black high resolution image signal; focal point detection means for detecting state of focusing in accordance with the electric signal transmitted from the image pickup means; and focal point control means for controlling the focal point adjustment lens in accordance with an output from the focal point detection means and as well as controlling the focal point adjustment lens in accordance with an output from the switching means to reduce the quantity of movement of the focal point adjustment lens in the second photographing mode as compared with a quantity in the first photographing mode.
According to another aspect of the present invention, there is provided an image pickup apparatus comprising: mode switching means capable of switching between a first photographing mode in which an electric signal transmitted from image pickup means is used to form a color natural image signal and a second photographing mode in which the electric signal transmitted from the image pickup means is used to form a white and black high resolution image signal; detection means for detecting whether or not focal point adjustment has been completed in accordance with a quantity of movement of a focal point adjustment lens in a predetermined time; lens control means for fixing the focal point adjustment lens in accordance with a result of detection performed by the detection means; and control means for controlling the detection means in accordance with an operation of the mode switching means in such a manner that a lens movement quantity in a predetermined time in the second photographing mode is smaller than that in the first photographing mode.
According to another aspect of the present invention, there is provided an image pickup apparatus comprising: photographing optical means; image pickup means for converting an optical image into an electric signal; lens position changing means for changing an optical axial directional position of a focal point adjustment lens with respect to the image pickup means; focal point evaluating value detection means for deducing, from an output from the image pickup means, a focal point evaluating value which is made to be a maximum value in a focused state; focal point control means which is capable of switching a lens movement quantity by the lens position changing means; photographing preparation processing means that operates at least the focal point evaluating value detection means to prepare a photographing operation; and photographing control means for performing main exposure under a condition set by the photographing preparation processing means to cause the image pickup means to photograph an object and making conditions for the image pickup means and the photographing optical means in the photographing preparation period caused by the photographing preparation processing means to be different from conditions set in the main exposure.
According to another aspect of the present invention, there is provided an image pickup apparatus comprising: mode switching means capable of switching between a first photographing mode in which an electric signal transmitted from image pickup means is used to form an image signal and a second photographing mode in which the electric signal transmitted from the image pickup means is used to form an image signal having a resolution higher than that of the image signal formed in the first photographing mode; focal point adjustment means that detects a state of focusing from an output from the image pickup means to adjust a focal point; and control means for controlling an operation of the focal point adjustment means in accordance with the mode switching means in such a manner that a unit movement of the focal point adjustment means in the second photographing mode is smaller than that in the first photographing mode.
As a result, the time required to reach the final focusing position can be shortened and thus the time taken to complete the focusing operation can be shortened.
By adequately switching the photographing mode in which the lens is moved considerably and the photographing release time lag is short and the photographing mode in which the lens is not moved considerably and precise focal point adjustment can be performed, the object can be photographed satisfactorily regardless of the state of the object.
Furthermore, an optimum focal point adjustment operation can be performed in both the color photographing mode and the precise white and black image photographing mode.
Other and further objects, features and advantages of the invention will be appear more fully from the following description.